Lubricant circuit

ABSTRACT

A lubricant circuit includes, but is not limited to a lubricant pump, which is connected on the suction side to a reservoir and on the pressure side to a distributor, at least one lubricating point, which is connected to the distributor and a return leading to the reservoir, and an electronic control unit, which is set up to regulate the output pressure of the lubricant pump by reference to the temperature of the lubricant.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application No.102010019007.1, filed May 3, 2010, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The technical field relates to a lubricant circuit, in particular forthe lubrication of an internal combustion engine such as an Otto ordiesel engine in an automobile.

BACKGROUND

Since the lubricant requirement of such an internal combustion engineincreases with its speed, the lubricant circuit usually comprises alubricant pump firmly coupled to an output shaft of the internalcombustion engine and driven by means of this. As a result of thiscoupling, the throughput of the lubricant pump increases with the speedof the internal combustion engine. Since the lubricant throughput of theengine is not exactly linearly proportional to the rotational speed, butdepends on other factors, in particular the temperature of the internalcombustion engine, the lubricant pump must be designed to provide asufficient amount of lubricant under all operating conditions. If theamount of lubricant conveyed by the pump is greater than the throughputof the internal combustion engine, the pressure at the output of thelubricant pump and an oil gallery connected thereto, which leads to theindividual lubricating points, and the proportion of the power of theinternal combustion engine, which must be applied for driving thelubricant pump, increases.

In order to prevent damage in the lubricant circuit due to too-highpressure at the output of the pump, it is usual to provide a pressurerelief valve directly at the output of the lubricant pump, via whichlubricant can flow back into a reservoir when the pressure at the outputof the pump exceeds a limiting valve. Such exceeding of the limitingvalue usually occurs when cold starting an internal combustion enginesince the pressure then increases substantially faster than incontinuous mode and the pressure at the pump outlet can shoot above thelimiting value before it has disseminated to a regulating devicedisposed downstream in the oil gallery and this is able to counteractit. For this reason the pressure relief valve is also designated as coldstart valve. The cold start valve certainly offers effective protectionfrom critically high pressures in the lubricant circuit but energy islost uselessly every time that the cold start valve lets lubricantthrough.

In order to be able to operate an internal combustion engineenergy-efficiently, it would therefore be desirable to have a lubricantcircuit which, on the one hand, is capable of supplying the internalcombustion engine with sufficient lubricant, but which on the other handcan restrict to a minimum or even completely avoid unnecessarily highlubricant pressures, which make it necessary to trip a cold start valve.If the occurrence of such a critically high pressure in the lubricantcircuit can be completely avoided, the cold start valve can also beomitted, which in turn leads to cost advantages.

In view of the foregoing, objects, desirable features andcharacteristics will become apparent from the subsequent summary anddetailed description, and the appended claims, taken in conjunction withthe accompanying drawings and this background.

SUMMARY

A lubricant circuit, in particular for an internal combustion engine,comprising a lubricant pump, which is connected on the suction side to areservoir and on the pressure side to a distributor, at least onelubricating point, which is connected to the distributor and a returnleading to the reservoir, and an electronic control unit for controllingthe operation of the pump, the control unit being set up to regulate theoutput pressure of the lubricant pump by reference to the temperature ofthe lubricant. Since the temperature of the lubricant can be determinedeven before starting the internal combustion engine, it is possible tosuitably predefine a desired output pressure of the lubricant pump atthe starting time of the internal combustion engine, so that pressurepeaks at the output of the pump, which must conventionally beintercepted via the cold start valve, can be avoided a priori.

According to a first embodiment, the control unit can be set up toestimate the temperature of the lubricant by reference to a model. Sucha model can, for example, estimate the lubricant temperature by usingthe behavior of the engine load in the past and optionally otherparameters. Naturally, the control unit can alternatively be connectedto a temperature sensor. Conventional automobile engines provide nosensors for detecting the oil temperature but measured values of acoolant water temperature sensor usually provided can readily be used toestimate the oil temperature. In order to be able to estimate the oiltemperature at least occasionally after the internal combustion enginehas been at a standstill for a fairly long time, an intake airtemperature sensor can also be used, which is present in any case inmany modern automobiles for controlling the mixture.

Since, at high temperature of the internal combustion engine (and thelubricant), the lubricant throughput of the internal combustion engineis generally high and the viscosity of the lubricant is low, it isexpedient to select the output pressure to be higher, the higher thedetected temperature. In practice, a simple threshold value control issufficient, at which the control unit sets a low or a high outputpressure of the lubricant pump depending on whether the detectedtemperature is below or above a limiting temperature.

Since the lubricant throughput of the internal combustion engine canalso depend on influences other than the speed and the temperature orcan be in a non-exactly linear relationship with the speed, it isexpedient to use a pump having a variable conveying rate as lubricantpump. Particularly preferred is a vane pump comprising a housing and arotor, whose eccentricity relative to one another can be varied underthe influence of the pressure prevailing in the distributor to controlthe conveying rate. In practice, the axis of the rotor of such a vanepump is preferably fixed in relation to a holder of the pump and achange of the eccentricity is effected by adjusting the housing of thepump relative to the axis of rotation in the radial direction.

A first actuator communicating with the distributor can expediently beprovided to drive the adjustment of the eccentricity. The actuator canin particular act on the one hand on the housing and on the other handon the rotor of the lubricant pump or on the holder.

In order to make the output pressure of the vane pumptemperature-dependent, the electronic control unit preferably controls avalve, which optionally connects to the distributor or separates fromthe distributor a second actuator, which is disposed to adjust theeccentricity of the lubricant pump. If both the first and the secondactuator are provided on the lubricant circuit, they are thenexpediently disposed so that they adjust the eccentricity of thelubricant pump in the same direction. If both actuators mutually supporteach other in this manner, a lower pressure at the output of the pump issufficient to achieve a given change of the eccentricity and therefore agiven change of the conveying rate of the pump, than is the case if onlya single actuator is effective.

In order that the second actuator does not block the movement of housingand rotor toward one another when it is separated from the distributorby the valve, the valve is preferably designed as a directional valve,which in one position in which it separates the second actuator from thedistributor, connects it to the reservoir. Whereas the first actuator isgenerally connected to a downstream portion of the distributor in orderto ensure that a requisite pressure is reached there, the valve ispreferably connected to an upstream portion of the distributor to enablea rapid response of the second actuator to pressure fluctuations at theoutput of the pump. This is particularly expedient if a throttleelement, in particular a lubricant cooler and/or a lubricant filter, isdisposed between the upstream and the downstream portion of thedistributor, which effects a pressure drop from the upstream to thedownstream portion and/or delays the dissemination of a high pressurefrom the output of the pump to the downstream portion.

In order to ensure a sufficient lubricant supply with at the same timehigh safety from impermissible excess pressures under all operatingconditions of the internal combustion engine, it is expedient that thecontrol unit is set up to further regulate the output pressure of thelubricant pump by means of the speed of the internal combustion engine.For this purpose, it can be connected to a speed sensor on a shaft ofthe internal combustion engine.

The above-mentioned limiting temperature is then expediently a functionof the speed or, which amounts to the same thing, at every temperaturethere is a limiting speed below which the control unit sets the lowoutput pressure and above which it sets the high output pressure. Thelimiting temperature is expediently lower, the higher the detected speedor the higher the temperature, the lower the limiting speed above whichthe control unit switches to the high output pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 shows a block diagram of a lubricant circuit according to anembodiment; and

FIG. 2 shows switching characteristics of the control unit at differentstarting temperatures.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to application and uses. Furthermore, there is no intentionto be bound by any theory presented in the preceding background orsummary or the following detailed description.

FIG. 1 shows a schematic diagram of an oil circuit in an automobileengine. A vane pump 1 is connected via a suction line 2 to an oil sump3. A distributor connected to the vane pump 1 on the pressure sidecomprises a supply line 4, on which an oil filter 5 and an oil cooler 6are disposed in series, and a gallery 7 from which branch lines 8 branchoff to various lubricating points 9 of the engine such as bearings of acrankshaft 10. From the lubricating points 9 the oil runs back into theoil sump 3 unguided.

The vane pump 1 has in a manner known per se a housing 11 having acylindrical cavity, in which there is provided a rotor 12 having aplurality of vanes 13 held by positioning rings in contact with an innersurface of the housing 11, which divide the cavity into a plurality ofcells. The rotor 12 has a fixed axis of rotation, against which thehousing 11 can be moved transversely to the axis of rotation under theinfluence of a spring 14 and two hydraulic actuators 15, 16. Inpractice, this movement is usually a pivoting movement about an axisrunning parallel to the axis of rotation of the rotor, outside thehousing 11. The two actuators drive a displacement of the housing 11 inthe same direction, opposite to the driving direction of a spring 14,which can be envisaged as a compressive spring in the diagram in FIG. 1.The actuators 15, 16 are shown schematically in FIG. 1, in each casecomprising a cylinder and a piston which is displaceable in thecylinder, the piston acting on the housing 11 and the cylinder beingrigidly connected to a bearing of the axis of the rotor 12. In practice,the actuators are usually implemented as pressure chambers, which aredelimited on the one hand by a one-piece frame part not shown in FIG. 1and on the other hand, by outer surfaces of the housing 11, on which thepressure of the oil in the pressure chambers acts directly.

The spring 14 and the actuators 15, 16 are each disposed in such amanner that a force exerted by the spring 14 works toward an increase ofthe eccentricity of the rotor 12 in relation to the housing 11 andtherefore an increase of the conveying rate of the pump 1, pressure ofthe actuators 15, 16 on the other hand works toward a reduction of theeccentricity and the conveying rate.

A control chamber of the actuator 15 is connected via a measuring line17 to a downstream end of the gallery 7 so that the pressure prevailingin the gallery 7 also exists in the control chamber of the actuator 15and exerts a force acting against the spring 14 on the housing 11. Thecross-sectional area of the control chamber of the actuator 15 and thestrength of the spring 14 are matched to one another such that if thesecond actuator 16 is pressure less, an oil pressure of approximately 4bars is reached in the gallery in stationary operation.

When starting the engine, the gallery 7 is pressure less and the spring14 holds the housing 11 in a position of maximum eccentricity.Consequently, the conveying rate of the pump 1 is maximal when startingthe engine, which is also expedient per se on order to build up aneffective oil supply at all lubricating points 9 in the shortestpossible time. However, as a result of the low temperature of theengine, a high conveying rate of the pump 1 accompanied by highviscosity of the oil and a low volumetric flow requirement brings abouta temporarily too-high pressure which can damage components and whichmust therefore be avoided. In order to achieve this, the actuator 16 isconnected via a second measuring line 18 directly to the pressure outputof the vane pump 1. For this purpose the measuring line 18 is kept asshort as possible and preferably runs completely inside a structuralunit, in which the vane pump 1 and the two actuators 15, 16 arecombined. Whereas in practice it can take several seconds before a highpressure at the output of the vane pump 1 has disseminated over theentire distributor as far as the actuator 15, this pressure acts on theactuator 16 almost without delay. The cross-section of its controlchamber is exactly the same size as that of the actuator 15 so that ifboth actuators 15, 16 are pressurized, a pressure of 2 bar isestablished on the gallery 7 in the stationary state.

Even if on starting the engine, the pressure of the oil conveyed by thepump 1 has not yet propagated as far as the actuator 15, the actuator 16is effective to avoid critical pressure on the supply line 4, whichcould damage the oil filter 5.

In order to ensure sufficient lubrication of the lubricating points 9(e.g., bearings) at higher speeds, the gallery 7 should be able to reacha pressure of approximately 4 bars. For this purpose a directional valve19 is disposed in the measuring line 18, which is capable ofinterrupting the measuring line 18 and making the control chamber of theactuator 16 pressure less via a connecting line 20 leading to the oilsump 3. If the actuator 16 is pressure less, merely the actuator 15controls the conveying rate of the pump 1 or the pressure on the gallery7.

The directional valve 19 is controlled by an electronic control unit 21,which is connected to a temperature sensor 22 and a speed sensor 23. Thecontrol unit 21 is preferably implemented in the form of an additionalsoftware module of a program-controlled engine control unit (ECU) knownper se. Since such engine control units are conventionally usuallyconnected to a temperature sensor to detect the cooling watertemperature of the engine and a speed sensor, the control unit 21 can beachieved with minimal expenditure. The control unit 21 is programmed toinitially switch the measuring line 18 to transmitting for a short timewhenever the engine is started and thus apply pressure to the actuator16 from the output of the pump 1. The time of switching to the pressureless state of the actuator 16 depends on the speed of the crankshaft 10and on the measured temperature, as is shown in FIG. 2 by reference toseveral curves C1 to C8. C1 describes the behavior of the control unit21 at a temperature approximately of −30° C.: the control unit 21 onlyswitches the actuator 16 pressure less at an extremely high speedbetween approximately 5000 and approximately 6000 rpm in order toincrease the oil pressure in the gallery 7 from approximately 2 toapproximately 4 bars. The same switching threshold applies at atemperature of approximately −20° C. (C2). At approximately −10° C.(C3), the switching threshold is reduced to a value betweenapproximately 4000 and approximately 5000 rpm. The same value alsoapplies at a temperature of approximately 0° C. In the range ofapproximately 10 to approximately 20° C. (C5, C6), the switchingthreshold is reduced to approximately 3000 to approximately 4000 rpm andat temperatures of approximately 60° C. and above which occur incontinuous operation, the switching threshold is approximately 2000 toapproximately 3000 rpm (C7, C8). Since the pump 1 can therefore beoperated at reduced output pressure at standstill temperatures of theengine, the energy requirement for conveying a given amount of oil attimes when the oil requirement of the engine is low due to low speed,can be reduced, which allows additional energy savings when operatingthe oil circuit.

While at least one exemplary embodiment has been presented in theforegoing summary and detailed description, it should be appreciatedthat a vast number of variations exist. It should also be appreciatedthat the exemplary embodiment or exemplary embodiments are onlyexamples, and are not intended to limit the scope, applicability, orconfiguration in any way. Rather, the foregoing summary and detaileddescription will provide those skilled in the art with a convenient roadmap for implementing an exemplary embodiment, it being understood thatvarious changes may be made in the function and arrangement of elementsdescribed in an exemplary embodiment without departing from the scope asset forth in the appended claims and their legal equivalents.

1. A lubricant circuit, comprising: a reservoir; a distributor; alubricant pump connected on a suction side to the reservoir and on apressure side to the distributor; a lubricating point connected to thedistributor; a return leading to the reservoir; and a control unitconfigured to regulate an output pressure of the lubricant pump byreference to a temperature of a lubricant.
 2. The lubricant circuitaccording to claim 1, wherein the control unit is configured to estimatethe temperature of the lubricant.
 3. The lubricant circuit according toclaim 1, wherein the control unit is connected to a temperature sensor.4. The lubricant circuit according to claim 3, wherein the temperaturesensor is in thermal communication with cooling water.
 5. The lubricantcircuit according to claim 3, wherein the temperature sensor is inthermal communication with intake air of an internal combustion engine.6. The lubricant circuit according to claim 1, wherein the control unitis configured to adjust the lubricant pump for a low output pressuredepending on whether the temperature is less than a limitingtemperature.
 7. The lubricant circuit according to claim 1, wherein thecontrol unit is configured to adjust the lubricant pump for a highoutput pressure depending on whether the temperature is greater than alimiting temperature.
 8. The lubricant circuit according to claim 1,wherein the lubricant pump is a vane pump having eccentricity that isadjustable under influence of a pressure in the distributor.
 9. Thelubricant circuit according to claim 8, further comprising a firstactuator communicating with the distributor and configured to adjust theeccentricity of the lubricant pump.
 10. The lubricant circuit accordingto claim 8, further comprising a valve controlled by the control unit,the valve configured to connect to a second actuator to the distributor,which is disposed to adjust the eccentricity of the lubricant pump. 11.The lubricant circuit according to claim 9, further comprising a valvecontrolled by the control unit, the valve configured to separate asecond actuator separates from the distributor, which is disposed toadjust the eccentricity of the lubricant pump.
 12. The lubricant circuitaccording to claim 11, wherein the first actuator and the secondactuator are disposed to adjust the eccentricity of the lubricant pumpin a same direction.
 13. The lubricant circuit according to claim 11,wherein the first actuator and the second actuator are disposed toadjust the eccentricity of the lubricant pump in a same direction. 14.The lubricant circuit according to claim 10, wherein the valve is adirectional valve.
 15. The lubricant circuit according to claim 11,wherein the valve is connected to an upstream portion of the distributorand the first actuator is connected to a downstream portion of thedistributor.
 16. The lubricant circuit according to claim 15, furthercomprising a throttle element is disposed between the upstream portionand the downstream portion of the distributor.
 17. The lubricant circuitaccording to claim 16, wherein the throttle element is a lubricantcooler.
 18. The lubricant circuit according to claim 1, wherein thecontrol unit is further configured to regulate the output pressure ofthe lubricant pump based at least in part on a speed of an internalcombustion engine.
 19. The lubricant circuit according to claim 6,wherein the limiting temperature is a function of a speed.
 20. Thelubricant circuit according to claim 19, wherein the limitingtemperature decreases as the speed increases.